F A C 1 ~ I ~ DYNAMIQUES DE LA PERCEFHON 339

Au cours de l'expost, j 'ai montr6 au moyen de projections quelques cas d'une perception de solides s'~tablissant presqu'imn~diatement et d'objets de la vie courante, o~ l'envers des choses volumineuses est donn~ assez auto- matiquement, si l'on se pr~occupe de cet aspect. J'ai aussi montr~ quelques cas o~ la donnte ph~nom~nale pr~sente un aspect tridimensionnel, le champ de l'espace ambiant semblant comporter l'aspect ant~rieur d'une structLre assez nette et l'envers d'un solide qui demeure plus vague.

J'ai montr6 en outre des cas de facteurs dynamiques s'attachant et sc m~lant k la perception. Pcu t -~e faudrait-il parler pluttt d'un cours pheno- menal sp~q.fique, poss&lant des trai~s de la perception et des traits de la solution d'un probl/~me.

Pourvu que les observateurs aient ,.te motives/t ce sujet, ce qui apparait comme un obstacle/~ la perception (ie renvers dans le cas sus-dit entraine ie d~sir de la solution totale et implique, en outre, des besoins subordonr.~s /~ celui-ci, donnant lieu ~t la recherche de solutions provisoires et n~cessaires pour la solution finale. Ainsi une perception de solides ~ peu pros neuve est n~e en beaucoup de cas.

Outre ces constatations, j'ai parI~ de deux mgthodes exp~rimentales propres A provoquer un changement de la motivation des observateurs qui centrent leur attention sur la face post~rieure et par cons~luent invisibte d'objets solides et j'ai rep~du compte des r~sultats phinom~naux ob~em:s dans ces conditions.

LITTERATURE

Jo~ "NSZN, M., An intrc, ductory study of voluminal form perception. Nord. Psykol., Monogr,, 1954, No. 5.

, The experienced continuations of some three-dimensional for'ns. Acta Psychol. 1957, Xlil, 1-26.

VALUE FACTORS IN THE PERCEPTION OF MAGNITUDE

BY

H. TAJFEL

(Oxford University, Oxford, England)

Evidence for the existence of shifts in judgments of magnitude due to

motivational or value variables is fairly satisfactory. Experiments on over- estimation can be divided into two groups: those concerned with the p hysi- cal dimensions of the stimuli which are relevant to the differences in value

TFn~t~ 13

between them; and tltose concerned with physical properties of the stim~i which are in no app;trent way related to the value of the stimuli. Reports of negative results often originated from this second group.

The "relevant" experiments on ov,.-r-estimation dealt with series of sti- muli which varied concurrently in a~ least two dimensions: the physical, and the "dimension'" of value. This s~:rial nature of the arrangement of sti- muli has not sufficiently been taken into account, especially in view of the evidence concerning the effects that all elements of a series, present or absent, have on quarttitative judgments of its individual members. A conver- sion of the data from several experiments on coins shows that in the "value" series the differences in size between the stimuli tended to be more accen- tuated than the objectively id, ~ticel differences between the stimuli in "neutral" series. Similar resul~s have been obtained in some experiments on weights recently completed by the author.

This would accoutnt for some apparent contradictions in the results of vetrious experiment,q on over-estime:tion, and would provide at least a partial explanation of the phenomenon. As I have tried to show elsewhere, :~e positive ~xnd negative results from experiments on over-estimation

which dealt bo~h with "relevant" ~nd "irrelevant" physical dimensions, c~tn often be predicted with the he]p of some extensions of the present argument.

Accentuation of differences between the stimuli of a value series can be expected on various grounds: in the first place, sensitive discrimination l~twcen element:~ of a series in which changes in the physical dimension serve as cues for changes in value: is of greater importance to the subjects than in a series where such a relationship does not exist. Secondly, diffe- rences in value between the stimuli can sometimes be identified on the basis o] cues which do not originate exclusively from the physical d~mension which is being judged. In such cases, these differences may be expected to act as a second dimension, correlated with the first. There is some evidence that .his torm of multidimensionality leads to an improvement of discrimination along the series. Thirdly, long-standing association between dimensions often results in difficulty for the subjects to judge in terms of one dimension only, isolated from the total context.

The argument outlined here is applicable not only to some of the results in the studies on over-estimation. In many social situations in which some fGrm of quantitative judgment is involved, the stimuli are classified into distinct groups in such a way that there is a consistent relationship between a continuous physical dimension, and a discontinuous classification. Judg- rients of skin colour of Negroes and whites by prejudiced and non-prejudi-

FACTEUR$ DYNAMIQUE$ DE LA PERCEPTION 341

ced subjects are an example here. Instead of dealing, as before, with individual stimuli which differ concurrently in a physical attribute and the attribute of value, we have here gr3ups of stimuli which differ in precisely the same

manner. There are possibilities of combining in various ways classifications,

physical dimensions, and value. Thus, value may or may not be correlated with the physical dimension. A discontinuous classification, superimposed on the series, may or may not be such that one part of the physical series tends to fall consistently into one class, and the other into the other class. Then again, the classification itself, whether predictably related or not to the physical dimension, may or may not be of inherent value to the subject. Combining these possibilities in various ways results in the establishment of a number of possible series, most of which are representative of quanti- tative judgments in social situations, and about which predictions can be made.

One further application is to series in which a classification is superimpo- sed not on a physical dimension, but on a conti:auous abstract attribute of the stimuli, such as beauty, pleasantness, inteiTigence, etc. Here again, there can be various possible interactions between the classification and the continuous attribute; these interactions should yield judgmental results not different in principle from those discussed above.

THE ECONOMY OF' PERCEIVING

BY

JEROME S. BRUNER

(Harvard University, Cambridge, Mass.)

The aim of this paper is to e~mmine three functions played by perception in the adjustment of the organism to its environment. Perceiving, looked at from the functional point of view, may be viewed as a strategy whereby an organism uses information provided by stimulation to achieve certain objectives, or to strike a balance between various objectives. The first form of strategy discussed is the means whereby organisms regulate the intake of information--regulate it both with respect to amount of information achieved and kind of information. A second class of strategies is directed toward the regulation of disruptive environmental surprises by the matching of perceptual expectancies to the likelihood of occurrence of events-to-be-